Question: Simplify the following expression: $z = \dfrac{3}{10r} + \dfrac{1}{7r}$
Solution: In order to add expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $10r$ and $7r$ $\lcm(10r, 7r) = 70r$ $ z = \dfrac{7}{7} \cdot \dfrac{3}{10r} + \dfrac{10}{10} \cdot \dfrac{1}{7r} $ $z = \dfrac{21}{70r} + \dfrac{10}{70r}$ $z = \dfrac{21 +10}{70r}$ $z = \dfrac{31}{70r}$